(a) Field of the Invention
This invention relates to an apparatus for the production of a gaseous mixture composed mainly of hydrogen from a hydrocarbon or hydrocarbon mixture as a raw material.
(b) Description of the Prior Art
There is an increasing importance of fuel cells as a means of power generation. Accordingly, small-sized apparatus, which permit a reliable, simple and economical production of hydrogen as a fuel for fuel cells, are desired.
There have been made a variety of proposals of small-sized apparatus for converting hydrocarbons to hydrogen by steam reforming.
The prior art includes Japanese Patent Laid-Open Nos. 78983/1978, 79767/1978 and 79768/1978.
These laid-open patents disclose small-sized apparatuses for the steam reforming of hydrocarbons.
Specifically, there are disclosed steam reforming apparatus in each of which a plurality of reactors, each composed by packing a catalyst for the steam reforming reaction in the space between the opposite tube walls in a double tube consisting of an outer tube and an inner tube, are disposed densely in parallel in the combustion furnace section from which the heat required for the steam reforming reaction is supplied.
All of these apparatuses are so designed that the space is made as small as possible in the combustion furnace section and the heat of combustion generated by flame combustion in the combustion furnace section thus-miniaturized is imparted to a gaseous mixture comprising hydrocarbon(s) and water vapor flowing through the space among catalyst granules by way of the outer tube wall of each reactor through convection heat transfer or radiation heat transfer, thus permitting the steam reforming reaction to proceed.
There is, however, a limitation in minimizing the space of the combustion furnace section.
The heat radiation of a gas is extremely small as compared with that of a solid.
It is impossible to produce a heat flux necessary for the steam reforming reaction, unless the combustion flame and combustion gas of a high-temperature gas in the combustion furnace section have a considerable thickness.
Consequently, even in these prior art processes, solid materials, which are raised to high temperatures by being heated by the combustion flame and combustion gas and impart the necessary heat to the surface of the outer wall of each reactor, are packed partially in the space of the combustion furnace section.
The apparatus is constructed in such a way that fuel and air fed to the combustion furnace section are burned to produce flame in the space where the solid materials are not packed and thus impart the heat of radiation to the surface of the outer wall of the reactor and the combustion gas is then passed through a packed bed of the solid materials to heat the packed bed and thereby to heat the surface of the outer wall of the reactor which is kept in contact with the packed bed.
As a part of the prior art processes there may be mentioned Japanese Patent Laid-Open Nos. 16536/1984 and 77601/1986 previously applied by the assignee of the present invention.
Japanese Patent Laid-Open No. 16536/1984 is characterized in that a radiation plate having a large surface area is equipped in the interior of the inner tube in a tubular reactor.
Japanese Patent Laid-Open No. 77601/1986 is featured by the provision of fins or studs with large surface areas on the outside of the outer tube of a tubular reactor.